After working as a newspaper reporter, in 1954 Phelan went freelance and eventually wrote for more than 60 magazines, including Fortune, Time, and The Saturday Evening Post. His investigative reporting on corporate America was especially distinguished. His best-selling book, Howard Hughes: The Hidden Years (1977), was published to critical praise. He also wrote a memoir entitled Scandals, Scamps, and Scoundrels: The Casebook of an Investigative Reporter (1982).